1. Field of the Invention
The present invention is concerned with improvement in or relating to a pneumatic impact imparting tool and more particularly to a pneumatic impact imparting tool in which the mechanism for converting rotational movement of a pneumatic motor at a constant rotional speed into intermittent turning movement of an anvil is made integral with the motor.
2. Description of the Prior Art
To facilitate understanding of the present invention a typical conventional pneumatic impact imparting tool as disclosed in U.S. Pat. No. 3,174,597 will be described below with reference to FIGS. 4 to 7. Basically, the conventional pneumatic impact imparting tool is constituted by a combiantion of a pneumatic motor adapted to be rotated by compressed air, an anvil and a mechanism for converting rotational movement of the pneumatic motor into intermittent turning movement of the anvil. Incidentally, FIG. 4 is a vertical sectional view of the conventional pneumatic impact imparting tool.
As is apparent from FIG. 4, the rotational force transmitting means comprises mainly a pneumatic motor 10 and a hammer 12. Specifically, as seen in FIG. 5, the pneumatic motor 10 includes a column-shaped rotor 14 having a shaft 13 extended therethrough, a cylinder 16 surrounding the rotor 14, a rear plate 18 secured to the lower end of the cylinder 16 and a front plate 20 secured to the upper end of the same to airtightly close the cylinder 16. To allow for rotation of the shaft 13, both the rear plate 18 and the front plate 20 are fitted with bearings 22 and 23. The rotor 14 is formed with a plurality of radially extending grooves 24 in an equally spaced relationship on the outer circumference thereof and each of the grooves 24 extends in parallel with the shaft. Further, a vane 26 is inserted in each of the grooves 24 in such a manner that it slides in the radial direction relative to the shaft 13. The shaft 13 of the rotor 14 projects through the front plate 20 and the part of the shaft 13 projecting outwardly of the front plate 20 is formed with a plurality of spline teeth 28. Importantly, the inner space of the cylinder 16 is so designed that the center axis of the hollow space is located offset from the center axis of the outer wall of the cylinder 16. Owing to the eccentric construction of the pneumatic motor 10, the rotor 14 is rotated by means of the vanes 26 as compressed air is introduced into the hollow space between the cylinder 16 and the rotor 14 by utilizing known means.
The hammer 12 includes an anvil 34 adapted to be intermittently turned by rotation of the motor 10 and means for converting rotation of the motor 10 into intermittent turning movement of the anvil 34. Further, the hammer 12 includes a cylinderical cage 36 having a closed lower end. A central opening through the closed end of the cage 36 is formed with a plurality of internal spline grooves adapted to engage the spline teeth 28 on the shaft 13 of the rotor 14. Since the cage 36 engages the rotor 14 via the splines it is caused to rotate at the same rotational speed as that of the rotor 14. The anvil 34 is formed with a plurality of spline teeth 38 at its lower end as seen in the drawing. As is best seen in FIG. 7, wings 40 extending in the leftward and rightward directions in the drawing are made integral with the anvil 34 at diametrically opposed positions. Both the spline teeth 38 and the wings 40 are accommodated in the interior of the cage 36. A spindle guide 42 against which the lowermost end of the anvil 34 abuts is secured to within the bottom of cage 36. An annular groove is formed on the outer surface of the spindle guide 42 facing the inner wall of the cage 36. A ball 44 is disposed at a predetermined position on the annular groove (at a predetermined position where it turns together with the cage 36).
A cam member 46 as shown in FIGS. 6 and 7 has a cylindrical configuration and a plurality of spline grooves adapted to come into engagement with the spline teeth 38 on the anvil 34 are formed on its cylindrical inner wall. The cam member 46 is adapted to slide axially with respect to the anvil 34 while maintaining engagement with the spline teeth 38 of the anvil 34. The lower end part of the cam member 46 constitutes cam face 48 with which the ball 44 is brought in contact and the cam face 48 exhibits a hill-shaped contour as seen from the side. Further, an outwardly projecting annular boss portion 50 is integral with the cam member 46 around its outer cylindrical surface. As shown in FIG. 8, the cage 36 is formed with two semicylindrical grooves 53 which accommodate 52 for sliding in the axial direction. Each of the pins 52 is formed with an annular recess 54 which comes in engagement with the annular boss portion 50 of the cam member 46. Accordingly, the pins 52 are caused to slide along the grooves 53 on the cage 36 as the cam member 46 is slidably displaced up and down. Further, a spring 56 is disposed in the hollow space between the surface of the cam member 46 located opposite to the cam face 48 and the wings 40 whereby the cam member 46 is normally urged toward the motor 10 under the effect of the resilient force of the spring 56. A cover 58 is tightly fitted into the top opening of the cage 36 in order to retain and the anvil 34 from within cage 36.
Next, description will be made below as to how rotational movement of the rotor 14 at a constant rotational speed is converted into intermittent turning movement of the anvil 34. As the rotor 14 is rotated, the cage 36 is caused to rotate and the ball 44 accommodated at the predetermined position in the cage 36 turns together with the cage 36. When the ball 44 comes in contact with the one inclined part of the cam face 48, the cam member 46 is slidably displaced toward the wings 40 by means of the ball 44 against resilient force of the spring 56. As the cam member 46 is slidably displaced in that way, a pair of pins 52 are also slidably displaced toward the wings 40 together with the cam member 46. As a result, the upper part of each of the pins 52 is projected upwardly into the area through which the wings 40 rotate. When the cage 36 (pin 52) is rotated to the point where the pins 52 are moved upwardly, the pins 52 are brought in abutment against the wings 40, causing the anvil 34 to be turned (see FIG. 7). Thereafter, the ball 44 moves over the hill top of the cam face 48 and thereby the cam member 46 is slidably displaced downwardly to the original position under the resilient force of the spring 56. At the same time the pair of pins 52 are displaced downwardly to the position where they do not contact the wings 40.
The cam member 46 does not slide axially until the ball 44 again contacts the inclined part of the cam face 48 after has moved over the hill top of the same. Then, the same operation as mentioned above is repeated when the ball 44 comes in contact with the inclined part of the cam face 48.
As will be readily apparent from the above description, the conventional pneumatic impact imparting tool is so constructed that the ball 44 carries out planetary movement as the motor 10 is rotated, the cam member 46 is slidably displaced in the axial direction by means of the ball 44, a pair of pins 52 are also slidably displaced in the axial direction in accordance with sliding movement of the cam member 46 and then the anvil 34 is intermittently turned by impact of the pins 52 against the wings 40 of the anvil 34. Namely, the cam member 46 is slidably displaced by means of the ball 44 and the pins 52 are then caused to slide together with the cam member 46.
Due to the above described, the length as measured from the ball 44 to the anvil 34 is equal to summation of the length of the cam member 46 and the length of the pins 52 (excluding the length of the area where the cam member 46 partially overlaps the pins 52 partially). As a result, the whole axial length of the pneumatic impact imparting tool is extended to accommodate.
As mentioned above, the anvil 34 is subjected to impact by pins 52. The small diameter of the pins 52 and the annular recess 54 for slidably displacing them while they are operatively engaged with the cam member lead to another drawback, i.e. breakage of the pins 52, particularly at the annular recess 54 of each of the pins 52.